+1 for the suggestions of checking spacers and BB shell facing. As for maintaining a HT bb you can just use a thin blade to remove the seals, flush and re-lube and it should last for many, many miles. You can even do this while it's still on the bike but of course it's good to remove the BB and grease the threads every so often to prevent corrosion. Mine has 26K miles on it and feels like new. You also mentioned the crankset was purchased used. Has it been carefully inspected for any issues such as the axle coming loose from the DS crank or a microscopic bend or bearing surface ovalized or not perfectly smooth?